Process of cleaning wire



Patented Aug. 4, 1931 UNITED STATES PATENT OFFICE CARL JOHN WARNKE, 0FELKHART, INDIANA, ASSIGNOR, BY MESNE ASSIGNMENTS,

TO MINNEAPOLIS-HONEYWELL REGULATOR COMPANY, OF MINNEAPOLIS, MINNE- SOTA,A CORPORATION OF DELAWARE PROCESS OF CLEANING WIRE No Drawing.

My invention relates to a process of cleaning wire especially the red orcopper clad wire employed as lead-ins of mercury switches.

In the manufacture of mercury switches the lead-in wires which aresealed through the glass envelope or casing of the switch and which arewelded to the electrodes that cooperate with the mercury switch are, ofcourse, subjected to high temperatures during the manufacture of theswitch. The portions of the lead-in wires which project exteriorly ofthe switch become coated or covered With oxides and other impuritiesduring the manufacturing operations and after the switch has beencompletely manufactured it is necessary to clean these wires thoroughlybefore tinning the same. The usual method that has been resortedto forcleaning the exterior portions of the leading-in wires has been tomechanically scrape the same. This operation is slow, laborious, andunlesscarefully carried out will set up cracking strains in the glassthat is sealed around the inner portions of the lead-in wires.

One of the principal obj ectsof the present, invention is to provide aprocess of cleaning the exterior portion of copper clad or red lead-inwires of mercury switches chemically and in such manner that theoperation may be speeded up, the amount of labor required greatlyreduced, and liability of the seal-ins around the wires being strainedor cracked avoided.

In carrying out the present invention the mercury switches, after beingcompletely manufactured, are carefully placed in a perforated hardrubber basket so that a large number of switches may be processed at thesame time. The loaded basket is then successively dipped in tankscontaining baths or solutions of hydrochloric acid, nitric acid, andsodium ammonium borate, the switches being washed and rinsed in runningwater following each dipping operation.

In the first dipping, the hydrochloric acid digests and removespractically all' of the oxides which occur as a scale or coating on thewire. Preferably the hydrochloric acid utilized inthe first dipping hasa specific gravity of 1.18 and the switches and their Application filedMarch 10, 1930. Serial No. 434,498.

wires are immersed therein for approximately forty seconds. After suchimmersion the loaded basket is lifted out of the hydrochloric acidsolution, drained and then dipped in running water to remove all tracesof the hydrochloric acid.

The second dippingoperation in nitric acid dissolves the chlorides thatmay be formed on the surfaces of the wires and also has the property ofdigesting any remaining oxides so that when the switches and their wiresare removed from the nitric acid the wires are thoroughly cleaned andtheir surfaces are clear of oxides and are bright and shiny. The nitricacid utilized preferably has a specific gravity of 1.42 and the switchesand their wires are immersed therein for a period of about ten seconds.

It is preferable to preserve this sequence of acid dipping, that is,first in hydrochloric acid and then in nitric acid, for the reason thatthe hydrochloric acid has a more uniform action on the entire surface ofthe oxide covered wire. If the nitric acid were used first it would tendto eat in certain parts more than others and thereby leave a pitted ornon-uniform surface.

After being lifted out of the nitric acid and drained, the mercuryswitches may be washed or may be immediately placed in a 20% solution ofsodium ammonium borate for approximately five seconds, the latteroperation being preferable. Sodium ammonium borate neutralizes any acidtraces that may occur in the pores of the metal, small crack." in theglass, or the like, and also prepares tne copper surface so that it isnot readily oxidized when brought out into the air. The ammonium in thesodium ammonium borate solution has the characteristic of dissolving anycopper oxide that may be formed by the action ofthesodium borate. Thesodium borate forms a microscopic film of copper oxide on the wires butthis film is converted into ammonium sodium cuprate which is soluble inwater and is taken off in the final rinse or washing. leaving a brightor seemingly highly polished surface which is well adapted for thetinning operation. It is to be understood that following the immersionin the sodium 'ammonium borate, the basket containing the mercuryswitches is lifted out of the solution, drained, and then rinsed underrunning water for at least ten seconds. The tubes are then driedpreferably in a drier although atmospheric drying may be suificient.

The projecting portions of the lead-in wires after being subjected tothis process have a surface which might be termed a nonacid skin whichis not readily oxidized in the air and which maintains the surfaces ofthe lead-in wires in proper condition for the tinning operation whichimmediately follows the process;

The tinning operation consists in dipping the lead-in Wire in a moltenbath of tin or solder.

The sodium ammonium borate solution is prepared by dissolving 10 arts(by weight) of ammonia and 10 parts by weight) of sodium borate in parts(by weight) of water.

I claim: v

1. The hereindescribed process of cleaning the lead-in wires of mercuryswitches which consists in dipping the switches and the wiressuccessively in hydrochloric acid, nitric acid, and sodium ammoniumborate.

2. The hereindescribed process of preparing the lead-in wires of mercuryswitches for tinning which consists in first dipping the switches andtheir lead-in wires in a solution of hydrochloric acid, then removingthe switches and rinsing them in water, then dipping the switches in asolution of nitric acid, next removing the switches from the nitric acidand rinsing them in water, then dipping the switches in a solution ofsodium ammonium borate, and finally removing the switches and theirlead-in wires from the sodium ammonium borate and rinsing them in water.

3. The hereindescribed process of preparing the lead-in wires of mercuryswitches for tinning which consists in first dipping the wires in asolution of hydrochloric acid having ai specific gravity ofapproximately...,

1.18 for approximately forty seconds, then rinsing the wires with water,then dipping the wires in a solution of nitric'acid having a specificgravity of 1.42 for approximately ten seconds, then dipping the wires ina 20% solution of sodium ammonium borate for approximately five secondsand then rinsing the lead-in wires in water for approximately tenseconds and then drying the lead-in wires.

In witness whereof, I hereto aflix my signature.

CARL JOHN WARNKE.

